Magnetic Flux Closure Directly Induced by Interplanetary Shocks: Observations 
Using IMAGE-FUV and SuperDARN, and Modelling With GUMICS-4.

Hubert, B.A., Palmroth, M., Milan, S.E., Janhunen, P., Kauristie, K., 
Cowley, S.W., Pulkkinen, T I., Gerard, J.


A method has been developed to monitor the dayside and nightside reconnection
rates using FUV remote sensing of the proton aurora and ionospheric convection
patterns. Global images of the proton aurora are obtained using the SI12
instrument of the FUV experiment on board the IMAGE satellite, and used to
identify the open/closed (o/c) field line boundary. SuperDARN data are used to
determine the ionospheric convection velocity, and the associated electric
field. The dayside and nightside reconnection voltages are then determined
accounting for the ionospheric electric field and the motion of the o/c
boundary. This method is used to compute the dayside and nightside reconnection
voltages during two interplanetary shocks for which the IMF was mostly
northward, so that the amount of open magnetic flux was so small that no
significant substorm expansion phase could develop. The flux closure voltage
shows a sharp signature when the interplanetary shocks sweep by the nightside
magnetosphere. MHD simulations conducted using the GUMICS-4 model for similar
conditions show a similar signature in the nightside flux closure rate. We
suggest that this flux closure event is directly induced by the compression of
the magnetotail.

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Fall Meeting, American Geophysical Union, San Francisco, U.S.A., 
5-9 December 2005